[BUGFIX] Install Tool fatal with Oracle database

Installing TYPO3 with an Oracle database (oci8) fails.
After selecting oci8 and passing the credentials,
the install wizard crashes with:

PHP Fatal error: Cannot use object of type
TYPO3\CMS\Core\Configuration\ConfigurationManager as array in
typo3/sysext/install/Classes/Controller/Action/Step/DatabaseConnect.php
on line 93

Obviously $config got mixed up with $configurationManager.
Fix this typo.

Resolves: #56253
Releases: 6.2
Change-Id: I58c1bc27f56b9a527d1d8fde7cf39b4ecd3ef7b6
Reviewed-on: https://review.typo3.org/27846
Reviewed-by: Markus Klein
Tested-by: Markus Klein
Reviewed-by: Wouter Wolters
Reviewed-by: Steffen Müller
Tested-by: Steffen Müller